Selenium Analogues

Selenium di-imides (132) were formed in methylene chloride solution from selenium tetrachloride with t-butylamine or sulphonamides and also from selenium metal with anhydrous Chloramine-T. They were found to be efficient reagents for the allylic amination of alken and alkynes. The first examples of selenium imides (133) were synthesized from diaryl selenides and Chloramine-T, from 

Condensation reactions of iV-sulphinylarenesulphonamides with diaryl selenones afforded iminoselenones of type (134) in excellent yields, the structures of which were confirmed by i.r. and electron spectroscopic studies.  

---

The stability of this derivative is attributed to the strong mesomeric effect of the NMca group, which changes the nature of the N=S bond. The selenium analogues RNSe have only been detected as transient species. 

The MS2N2 complexes and their selenium analogues are readily protonated at the nitrogen attached to the metal (Eq. 7.5). Competitive studies show that the selenium complex is a stronger base than its sulfur analogue. 

Selenium analogues RN=SeCl2 are unknown for R = aryl or alkyl and thermally unstable when R = CE3 or C2E5. The perfluoroalkyl derivatives are prepared by the reaction of dichloroamino compounds and Sc2Cl2 in CCI3E (Eq. 8.18), but they decompose at room temperature to the corresponding diazene and a mixture of selenium chlorides. 

A more versatile synthesis of 11.1 (and the selenium analogue) involves the cyclocondensation of trisilylated amidines with sulfur dichloride or SeCl2 generated in situ (Eq. 11.3). This route can be used to prepare the prototypal systems [HCNEEN]" (E = S, Se). It is also readily extended to the synthesis of multi-dichalcogenadiazolium cations such as 1,3- or 1,4-C6H4(CNEEN)2] (H-2, E = S, Se), °... 

The selenium analogue [PhCNSeSeN] and cyano-functionalized diselenadiazolyl radicals adopt cofacial dimeric structures, e.g., 11.4 (E = Se), with unequal Se Se interactions of ca. 3.15 and 3.35 A. In the latter case the radical dimers are linked together by electrostatic CN Se contacts.Tellurium analogues of dithiadiazolyl radicals (or the corresponding cations) are unknown, but calculations predict that the radical dimers, e.g., 11.4 (E = Te), will be more strongly associated than the sulfur or selenium analogues. ... 

The UV absorption spectrum of benzoisotellurazole is similar to those of its sulfur and selenium analogues, all absorption bands of the former being bathochromi-cally shifted relative to the latter compounds. The NMR signal of the H-3 proton... 

Sulfur and selenium analogues of 91 are also susceptible of this type of rearrangement. Its rate is defined by the strength of the C-chalcogen bonds in 91 and analogues and was found to increase in the order of S < Se < Te (94MI1). 

Mass spectra of l,6-dioxa-2,5-diaza-6<2-tellurapentalenes are given in (75JHC639). The ESCA spectra of the parent heterocycle and of its sulfur and selenium analogues were discussed (80JA1783). 

Metzner et al. also prepared the selenium analogue 17 of their C2 symmetric chiral sulfide and tested it in epoxidation reactions (Scheme 1.6) [8]. Although good enantioselectivities were observed, and a catalytic reaction was possible without the use of iodide salts, the low diastereoselectivities obtained prevent it from being synthetically useful. 

Scheme 7 Examples of ortho-diiodo TTFs and selenium analogues used in cation radical salts...

The most common binary systems are the tetramers S4N4 and Se4N4. Sulfur or selenium analogues of the monomeric species NO or N02 are thermally unstable. 

---